The composition of the combustible air-fuel mixture in the combustion chamber is of decisive importance for fuel consumption as well as for the pollutant content of the exhaust gas. Precise controlling of the mixture formation is very important, especially for internal combustion engines tuned for lean operation. The following fuel metering methods are known and usable for internal combustion engines having external mixture formation:
The fuel metering can take place in a cylinder-selective manner by feeding the fuel into individual intake pipes leading to the individual cylinders by means of fuel injection values disposed close to the intake valves. These fuel injection valves usually function such that they can be switched between two positions—valve “fully open” and valve “fully closed”—and the injected fuel quantity is changed exclusively by manipulating the time duration of the opening as well as, if desired, by manipulating the phase position of this opening relative to the phase position of the opening of the intrinsic intake valve. As a result, it can rapidly respond to varying quantity demands, i.e. the system operates highly dynamically. Due to the fact that the mixture mass flowing into the cylinder proceeds as a function in accordance with the piston movement, which piston movement is predetermined by the crankshaft design, the fuel mass flow remains constant at a constant load, but a relatively inhomogeneous mixture composition results inside the combustion chamber. At the lean operating limit, this leads in particular to large standard deviations in the cylinder mean effective pressure and to high NOx-emissions.
In the other fuel metering methods, the fuel metering takes place remotely in a manner centrally for all cylinders and relatively far from the intrinsic intake valves. Consequently, a buffer volume exists between the fuel metering location and the intake valves, whereby a good homogeneity of the inflowing air-fuel mixture is in fact achieved, but wherein the dynamic capability is restricted due to the long way between the fuel metering location and the intake valves, i.e. the composition of the inflowing air-fuel mixture can be adapted to the varying demands only with a certain lag.